There is a male/female nut extending the centre channel (consumer side). It clamps the sandwich in place and provides threads for the filter (or the next sandwich if you have a separate one for sensors) to thread on to.

On mine there never was a hex nut. The sandwich plate to the oil cooler is just held in place when the oil filter is installed. When the filter is removed, the plate can be removed as well. It has always worked OK. Maybe the nut was lost by the P.O.? The parts manual does not show any nut.

OK....as an alternative, is the centre of the attaching fitting machined as a hex so as to allow the use of an allen wrench to tighten it? I can't see the oil filter fitting just being screwed in by hand....then again it is British....I can see them using the filter as a nut to hold the whole mess together ...guess I should just pull the filter and get a mirror....Tomorrow's project...thanks for trying

Bfitz241 wrote:Thanks for the picture. So the oil filter holds the whole thing together...got it
Bingo !
Without the sandwich plate in place, there is a short length of threaded pipe screwed into the Auxiliary Housing. It's long enough to stick out 'about' one inch when fully seated. The oil filter screws onto that threaded stub, and tightens securely in place.

With the sandwich plate, that threaded stub is too short, and wouldn't stick out for the filter to thread on. So, it's is first removed, then the male-female threaded extender, item 13 in the drawing above, is screwed into the Aux Housing. Then the original male threaded pipe is screwed into the adapter.

The extender/ adapter is approximately as long as the sandwich plate is thick. So with the S-plate in place, the male threaded stub still has about the same exposure it had without the S-plate. Spin the oil filter on and tighten it down. The oil filter then acts as the nut that pulls the assembly together, sealing the joints on both sides.

The oil filter has a square rubber O-ring that seals against the outside of the Sandwich Plate, and the S-Plate has a similar O-ring that seals against the Aux Housing. Both O-rings must be in place. The oil filter's O-ring is replaced along with each new oil filter. However, the sandwich plate's O-ring is often allowed to age and lose effectiveness. It should also be replaced periodically.